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Combined effect of ryegrass and Hyphomicrobium sp. GHH on the remediation of EE2-Cd co-contaminated soil

He, Shanying, Li, Yuan, Guo, Haihui, Lu, Li, Yang, Chunping
Journal of soils and sediments 2020 v.20 no.1 pp. 425-434
Hyphomicrobium, Lolium, bioaccumulation factor, cadmium, crops, edaphic factors, enzyme activity, heavy metals, hormones, human health, irrigation, microbial carbon, phytoaccumulation, phytomass, polluted soils, root growth, roots, shoots, soil enzymes, soil remediation, urease
PURPOSE: Irrigation and fertilization accelerate the accumulation of environmental hormones such as 17α-Ethinyestradiol (EE2) and heavy metals such as Cd in soil, which in turn harms crops and human health. The objective of this study was to investigate the interaction of the plant ryegrass and EE2 degrading bacteria Hyphomicrobium sp. GHH on the remediation of EE2-Cd co-contaminated soil. MATERIALS AND METHODS: The concentration of EE2 in soil was set as 25 mg kg⁻¹, and the concentration of Cd was set as 0, 5, 20, and 80 mg kg⁻¹, respectively. Pot experiments were carried out to investigate the control treatment without GHH inoculation and/or ryegrass cultivation (C), GHH inoculation alone (B), ryegrass cultivation alone (P), and combined use of ryegrass with GHH (B + P) on the EE2 and Cd removal from soil. The plant biomass, EE2 and Cd concentration in root and shoot of ryegrass, the bioconcentration factor (BCF), translocation factor (TF), phytoextraction efficiency of EE2 and Cd, and removal rate of EE2 and Cd from soil, as well as the soil urease activity and microbial biomass carbon (MBC) content, were determined to evaluate the interaction of plant and microbe on the soil remediation. RESULTS AND DISCUSSION: After 28 days of treatment, in soil with spiked Cd at 5, 20, and 80 mg kg⁻¹, the removal rate of EE2 from soil was: B + P > P > B > C; the effect on the Cd removal was B + P > P, while Cd cannot be removed by microbes directly. In B + P treatment, the removal rate was 89%, 80%, and 71%, respectively for EE2, and 0.81%, 0.43%, and 0.38% respectively for Cd. EE2 and Cd were mainly stored in root of ryegrass because that all the TFs were < 1. The inoculation of GHH significantly promoted plant growth and substantially increased the extraction efficiencies of EE2 and Cd by ryegrass (P < 0.05). Both cultivation of ryegrass and inoculation of GHH improved the soil environment, and the improving effect on the urease activity and MBC content was B + P > P > B > C. 5 mg kg⁻¹ Cd increased soil urease activity and MBC content, and promoted the root growth. However, soil Cd at the concentration > 20 mg kg⁻¹ caused irreparable harm to ryegrass and microorganisms; as the consequence, the EE2 extraction by plant significantly decreased (P < 0.05). CONCLUSIONS: The combined use of ryegrass with GHH was effective to remediate the EE2-Cd co-contaminated soil.